Transport installations with revolving belts are used, for example, as what are known as “discharge stations” and are described inter alia in U.S. Pat. No. 3,429,416 and EP-A-558 123. The purpose of these installations is to distribute a product stream having a multiplicity of products, for example chocolate bars or biscuits which are mostly delivered directly from a production process, to a plurality of packaging machines.
In this case, the products are transferred from a main transport stream, in which they are moved, arranged in rows, by means of movable belt sections onto the individual feed devices, mostly arranged transversely to the main transport stream, of the individual packaging machines. A multiplicity of arrangements are known here, depending on the specific requirements, such as the demand for space, installation speed, product properties and operator friendliness and accessibility for cleaning and maintenance.
The broad belts used tend to run “obliquely”, and therefore a special device is needed to ensure the linear stability of the belts. Such a device of the type initially mentioned for a discharge station is known from EP-A-0 659 663. In this case, a pressure roller is arranged below the main transport belt. The pressure roller, which has a low loop-around, can be moved forward and backward on one side for the purpose of passive belt control. The belt is steered in a desired direction as a result of this movement.
The belt control known from EP-A-0 659 663 has the disadvantage that the control roller has only a low loop-around. Only limited influence upon the belt run is therefore possible. Moreover, the control roller acts upon the belt outside which, with progressive contamination, mostly allows ever lower friction or force transmission, and therefore the controllability of the belt is further impaired. Also, only reaching the two extreme positions of the belt edges is monitored by the sensor technology, and this is then reversed in each case, so as to give rise to a belt run which swings to and fro constantly between the two extreme positions. A further disadvantage arises in that the belt rollers are connected fixedly to the frame of the station. For this reason, to change a belt, the belt has to be cut open and the new belt has to be welded to the installation. Should an endless belt be changed directly, in this installation all the rollers around which the belt is looped have to be demounted.